Production of pitch from petroleum residues



R. D. BEATTIE PRODUCTION OF PITCH FROM PETROLEUM RESIDUES Filed Nov. 27, 1953 INVENTORL fiedfi'ee 1269K m8 z9S E W W mo xo5 zficw 2 k 5 1 Q. M3515: xN 5:51 \W\ (N I N W823i 1 $22 F 02:38 NW M65028 \m WW June 26, 1956 Unite PRODUCTION OF PITCH FROM PETROLEUM RESIDUES Robert D. Beattie, Arlington, Mass.,

L. Cabot, Inc., Boston, Mass., chusetts assignor to Godfrey a corporation of Massa- This invention relates to the production of pitch from petroleum residues and consists in a continuous process for producing from such residues valuable pitch products having particular utility as binders for carbon electrodes. In certain aspects this invention is an improvement over that described in copending application Ser. No. 335,544 of Cole et al., filed February 6, 1953.

Most carbon electrodes are manufactured from a suitable hard carbonaceous material, usually calcined coke. As the coke has no natural adhesiveness it must be bound together in suitable shapes with a compatible material. In making electrodes, the coke is ground, mixed with the binder, molded and baked to carbonize the binder. Several hundred thousand tons of binder are used annually in electrodes.

In the art of electrode manufacture it has been learned from experience that the nature and quality of the binder used is extremely critical. Petroleum tars and pitches have not heretofore proved to be generally useful as binders because of their high contaminant contents and poor coke yields and particularly because of their migration during baking of the electrode which leaves areas of unbonded carbon in the finished article. In this condition the electrode is of uneven mechanical strength and is variable in conductivity. Consequently, petroleum pitches have not heretofore been used to any extent as binders for electrodes and coal tar pitch has had a virtual monopoly for such usage.

Pitches suitable for binders and electrodes must fall within a fairly narrow range of specifications as follows:

Melting point Not above 120 C. Softening point Above 38 C.

Cr Not below 8% by weight. C11 Not below 30% by weight. Coking value Above 30%.

Of these specifications CI is the hydrocarbon fraction which is insoluble in nitrobenzene and C11 is the hydrocarbon fraction which is soluble in nitrobenzene but insoluble in acetone. Coking value is the percentage of material remaining after heating a sample of pitch for 7 minutes at 950 C. in a dry atmosphere. For further description of these specifications see Chemistry of Coal Utilization, published by John Wiley & Sons, 1945, vol. II, chap. 31 and in particular page 1310.

The pitch produced by the process of my invention falls within the above specifications and may be used interchangeably with coal tar pitch as an electrode binder. Petroleums do not meet these specifications and are not good binders.

It is the principal object of this invention to provide a commercially practicable, continuous process for converting petroleum residues to valuable pitch products.

It is a further object of this invention to provide such a process for the production of pitches having properties within the range of specifications set forth above.

It is a further object of this invention to provide such a process for the production of electrode binder pitch and valuable hydrocarbon by-products at high yields.

It is a further object of this invention to provide a continuous process for upgrading thermally cracked catalytic cycle residues to products having considerably enhanced values.

The process of my invention is particularly adapted to the production of hard pitches, so called because they melt in the upper temperature range, i. e., between about and F. The hard pitches make the best binders and hence are generally preferred to the soft pitches for binding electrodes.

The process of this invention may briefly be summarized as follows. Feed stock, which may be any thermally cracked catalytic cycle residue, is pumped through heaters, where its temperature is raised to about 800 to 1200 E, into a soaking tank of substantial capacity maintained under superatmospheric pressure. Flow is so regulated through the soaking tank that residence time for any given increment of feed stock is preferably between about 3 and 5 hours, the exact residence time for any given material being determined by the susceptibility of the stock to cracking. During soaking volatiles separate from the main body of the stock and are conducted to a distillation tower, being introduced into the rnidsection of the rectifying zone in the tower. The heavy liquid stock, which is withdrawn from the bottom of the soaking tank, is conducted to the section of the distillation tower between the rectification and stripping zones therein. Here the light ends (boiling below about 700 F.) flash up through the rectifying zone and the pitch flows downward through the stripping zone. Steam superheated to about 800 F. is introduced into the bottom of the tower and flows upward through the stripping zone countercurrent to the downward flow of pitch to remove whatever volatile matter may still be mixed with the pitch.

The pitch product collects in the bottom of the distillation tower. However, the first increment of product after initial start up is not of much value. Consequently, it is necessary to recycle this material through a heater to the soaking tank. Once in full operation, of course, only a portion of the pitch is recycled but it is this recycle in critical minimum ratio to pitch product recovered which is one feature of my invention.

The rectification section of the distillation tower functions in conventional manner. The light end vapors leave the top of the tower, are condensed, and a portion is returned to the top of the tower for reflux. These lighter hydrocarbons are thus rectified in accordance with known refining practice and are recovered for suitable use.

It will be apparent from the above general description of my novel process that I have provided means for producing valuable materials from low cost petroleum residues having otherwise little value except as industrial fuel.

My invention will now be described in greater detail with reference to the accompanying drawing which is a flow diagram of the process.

Petroleum residue raw material, also referred to herein as make oil or material, is withdrawn from a suitable storage tank 10 and delivered to preheater 12 by pump 14. In the preheater the make oil is heated to a temperature advantageously in the vicinity of 300 F. High pressure steam is a convenient source of heat at this stage. From preheater 12 the make oil flows through furnace 16 where it is further heated to a temperature of between about 800 and 1200 F. At the selected temperature the make oil is delivered at elevated pressure to insulated soaking tank 18 through conduits 20 and 22.

It is in the soaking zone that the make oil is converted to the pitch product after recycle has been established as hereinafter described. Hence it is necessary to retain the oil in the soaking zone for a sufiicient time to complete conversion. Residence time can be shortened and rate of conversion can be increased -by maintaining the soaking zone under superatrnospheric pressure, preferably of at least 30 lbs. per sq. in. guage (p. s. i. -g.). From observed effects it appears that the nature of the reaction occurring in the soaking zone at the temperature and pressure prevailing therein is cracking and further polymerization of the oil. Hence the residence time for soaking is somewhat variable as between make materials, the criterion being the product obtained, i. e., a pitch having the requisite Cr and C11 content and a suitable melting point, without forming any substantial amount of solid carbon.

During the soaking period, as I have said, cracking occurswhich results in the formation of substantial quantities of volatile hydrocarbons boiling below the temperature prevailing in the tank 18. These are permitted to leave tank 18 through conduit 24 and self-actuating pressure control valve 26 and are introduced into the midsection of the rectification section of a conventional distillation or fractionating tower 28 in which pressure is advantageously near atmospheric. Flow of volatiles will be essentially continuous since fresh make material is continuously supplied to soaking tanklfi. In distillation tower 28 the volatiles will be partially condensed but the greater proportion thereof will pass out of the tower as vapor through pipe 30. Accordingly, a condenser 32 followed by a water separator 34 are provided in the system. The volatile liquid is freed of its water in separater 34 and a portion is recycled'to tower 28 through pump 36 and conduit 38 while the remaining portion is recovered through pipe 40 as a by-product of the process. Water is eliminated through drain pipe 42.

The make oil is retained in soaking tank 18 for a sufficient time to effect the desired separation and conversion. The soaking time will ordinarily be about three to five hours but may be somewhat more or less depending upon the volume of available raw material in relation to the capacity of the soaking tank, the properties of the oil, etc. However, if there is any important departure from the 3 to hour period it willprobablybe necessary to adjust the temperature at which the make oilis delivered to the soaking tank. Thus, for a soaking time of say 6 hours the temperature of the make oil may haveto be reduced to 750 F. In any event suitable adjustments, such as in soaking tank pressures, pitch recycle'ratio, etc., can be made empirically to suit the existing conditions.

Since the process is continuous the make material will always be moving slowly through the soaking tank. Consequently, to achieve a reasonablyuniform residence time for all of the material it should be introduced "into the tank at the end opposite its discharge end. For this reason a vertically disposed tank which is long relative to its cross sectional area is preferred. As illustrated, delivery conduit 22 is connected into tank 18 near the top and a discharge conduit 44 is provided at the bottom. A pressure control valve 46 is provided in conduit 44 to regulate flow out of the tank.

Conduit 44 is connected into distillation tower 28 in the section immediately below the rectification section and above the stripping section. As the pitch flows into the tower most of the light ends remaining therein flash up through the rectifying zone where the 'downflowing condensate previously described serves to strip out any pitch entrained in the light end vapors and to carry it down into the stripping zone. Superheated steam is advantageously delivered to the bottom of the stripping zone through pipe 48 to remove whatever light ends may still be mixed with the pitch.

The pitch collectingin the bottom of distillation tower 28 is continuously withdrawn "through two pipes. One pipe,50, conducts away a portion of'thepitch as product and the other, 52, conducts the other portion as recycle material through pump fi i furnace 16 and conduits 56 and 22 to soaking tank 18.

As indicated above, a single pass through the soaking tank is not sufiicient to raise the C1 and C11 contents of the pitch to the requisite values. However, when the make material is commingled with pitch previously produced in the proper proportions, 'an equilibrium condition is reached in which-a-pitch of satisfactory properties is produced.

It is thus an essential feature of my invention to recycle a portion of the pitch product to the soaking tank and the bottom limit of recycle ratio is critical. At the convenientsoaking tank operating pressure of about 30 p. s. i. g. I have found that a -:pitch recycle to pitch recovered ratio of 0.8 is the operable minimum. However, at higher operating pressures lower recycle ratios may be used so that a 500 p. s. i. g. the ratio may be as low as 0.4. There is no top limit on recycle ratio so far as ability to'produce a satisfactory electrode pitch-is concerned provided conditions in the soaking tank are adjusted accordingly to avoid solid coke formation. But obviously a high recycle ratio is accompanied by low product recovery. Hence the preferred range of recycle ratios generally do not include values much above 2. As a general rule, the Cr and C11 contents and the melting temperature of the pitch are increased with increase in recycle ratio.

My invention will now be illustrated with reference to one commercial operation processing 3000 barrels per stream day of a petroleum residue having the following specifications: API gravity 60 F., 0.54; correlation factor, 126.8; cracking index, 600; molecular weight factor, 245 AST M midboiling point, 700 F.;' asphaltines, 7.5-8%.

Make material is delivered to the system at the rate of gals. per min. under a pressure of 150 p. s. i. g. In the preheater its temperature is further increased to about 1000 F. The oil then flows into thesoaking tank maintained at a pressure of 30 p. s. i. g. where it remains in slowmotion for 4 hours. During residence in the soak ing tank volatiles having boiling points below about 700 F. flash off the oil and are conducted to the distillation tower as previously described.

Pitch flows to the distillation tower at gals. per minute and is withdrawn therefrom in two streams, one of 70 gals. per'min. to product recovery and the other of 60 gals. per min. to recycle. Total volatiles delivered to the distillation tower amount to'200 gals. per min. of which gals. per min. are refluxed through-the tower and 70 gals. per min. are withdrawn as product.

Thus under the conditions above enumerated there is produced a totalof 238 tons of hard pitch-and 10,800 gals. of gas-oil per stream day.

It will be appreciated that operating conditions can be varied from the above. For example, the soaking tank may be maintained under a pressure of as high as 500 p. s. i. g. in which case make material will be fed under a pressure of about 620 p. s. i. g. The advantage of using high pressure in the soaking tank lies in the enhanced C1 and C11 contents of the product 'but a satisfactory product can be obtained at lower pressures which are easier to produce and maintain. Also the recycle ratio can be increased to well above the 'minimum operable value (0;40.8) -in order toin'c'rease both the melting temperatureand the (Brand C11 contents of the product. Here again, however,'is a balancing of conveniences "involved since higher recycle ratios are accompanied by lower production rates.

Having thus described my invention, I claim:

1. A process for producing pitch from petroleum which comprises heating a petroleum residual oil to above about 750 F., conducting the hot oil to a soaking zone, retaining the oil therein under super-atmospheric pressure for a'period of at least three hours, thereby converting the oil to the pitch and volatile by-products, conducting pitch and volatile by-products from said zone and recycling a portion of said pitch thereto at a ratio of recycle to product recovery volume of at least 0.4.

2. The process of claim 1 in which the residual oil is a thermally cracked catalytic cycle residue and is heated to about 800-l200 F.

3. The process of claim 1 further characterized by stripping the pitch of substantially all volatile materials prior to recycle.

4. The process of claim 1 further characterized by retaining the oil in the soaking zone for a period of about 3-5 hours and recycling pitch thereto in the ratio of 0.4 to 2.

5. A process for producing electrode binder pitch having a melting point in the range 105 to 120 C. and a C1 and C11 content of at least 8% and 30% by weight respectively, which consists in heating a thermally cracked catalytic cycle residual oil to about 800-1200 F. while in continuous flow, feeding the heated oil into a soaking zone, flowing the oil therethrough at a rate such that the average residence time of the oil therein is from about 3-5 hours while maintaining the oil under a pressure of 30 to 500 p. s. i. g., thereby producing volatile hydrocarbons and pitch, continuously conducting away from said zone in separate streams the pitch and volatile hydro carbons produced therein, separating the pitch stream into a recycle stream and a product stream in the ratio of recycle volume to product volume of at least 0.4, heating the pitch in the recycle stream to substantially the same temperature as that of the residual oil feed, flowing the recycled pitch into the soaking zone and recovering the pitch from the product stream.

6. The process of claim 5 further characterized by the intermediate step of introducing the volatile hydrocarbons and pitch into different zones in a distillation zone whereby to rectify the volatile hydrocarbons and to strip substantially all of the remaining volatiles from the pitch.

References Cited in the file of this patent UNITED STATES PATENTS 1,712,187 Wilson May 7, 1929 2,305,440 Noel Dec. 12, 1942 2,633,449 Cheney Mar. 31, 1953 2,662,051 Pelzer Dec. 8, 1953 

1. A PROCESS FOR PRODUCING PITCH FROM PETROLEUM WHICH COMPRISES HEATING A PETROLEUM RESIDUAL OIL TO ABOVE ABOUT 750* F. CONDUCTING THE HOT OIL TO A SOAKING ZONE, RETAINING THE OIL THEREIN UNDER SUPERATMOSPHERIC PRESSURE FOR A PERIOD OF AT LEAST THREE HOURS, THEREBY CONVERTING THE OIL TO THE PITCH AND VOLATILE BY-PRODUCTS, CONDUCTING PITCH AND VOLATILE BY-PRODUCTS FROM SAID ZONE AND RECYCLIC A PORTION OF SAID PITCH THERETO AT A RATIO OF RECYCLE TO PRODUCT RECOVERY VOLUME OF AT LEAST 0.4. 